Often thought of nostalgically as the ultimate shelter of childhood, the treehouse has made a strong push into adulthood with eye-popping locations and aesthetically-pleasing, luxurious designs. Over the past few months alone, we've seen the Hemloft, Redwoods Treehouse and EcoPerch, among a few others. Now, there's the ErlebNest - a German-designed treehouse situated within a high ropes course.